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FETS as volt. controlled resistance

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LeftRights

New Member
I want to use a FET as a Voltage controlled resistor for the RC circut in a monostable multivibrator. With the FET handle 5v? What kind of FET handles the most voltage? Is there anything that I can use that will handle 5V.

Also, the multi- vibrator is already there so I can't replace it with anything (ie VCO's).

Help would be greatly appreciated.
 

Roff

Well-Known Member
While it's true that a FET can be used as a VCR, they only work well in small-signal applications. For large signals such as those encountered in a multivibrator, I don't think you will be pleased with the results. A voltage-controlled current source is a much better choice. What type of monostable multivibrator (AKA one-shot) are you using? Can you post an IC part number, or better yet, a schematic?
 

Optikon

New Member
Oh yeah and FYI, you can get FETS that handle from 10V to many thousands of Volts so don't worry 'bout that.
 

LeftRights

New Member
Optikon said:
Oh yeah and FYI, you can get FETS that handle from 10V to many thousands of Volts so don't worry 'bout that.
is this true? can they handle +/-5v working as voltage controlled resitors? I heard that they were limited to millivolts...
 
+/- Supplies

I think for the +/- you must use not a simple JFET but a MOSFET.
 

Roff

Well-Known Member
As I said previously,
Ron H said:
While it's true that a FET can be used as a VCR, they only work well in small-signal applications. For large signals such as those encountered in a multivibrator, I don't think you will be pleased with the results. A voltage-controlled current source is a much better choice. What type of monostable multivibrator (AKA one-shot) are you using? Can you post an IC part number, or better yet, a schematic?
 
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